Background: Blast-related traumatic brain injury (bTBI) presents a significant concern for military personnel and veterans. The most common bTBI-associated problems are cognitive deficits (executive functioning, attention and memory) and neuropsychiatric issues (sleep disturbance and PTSD), a debilitating combination affecting cognitive, social and occupational functioning. Early and effective treatment could help reduce the societal and personal costs of bTBI and related sequelae. However, there are no evidence-based protocols available to address multiple cognitive impairments and neuropsychiatric symptoms in returning veterans with bTBI. Objective: To address the current therapeutic gap we propose a novel therapeutic approach for treatment of multiple chronic bTBI-related impairments. Noninvasive brain modulation, such as the application of red and near-infrared light utilizing light-emitting diodes (LED) to the head, hs been shown to improve cognitive (executive and memory) function and to induce improvements in neuropsychiatric symptoms (sleep, mood, and PTSD) in civilian populations. We hypothesize that LED treatment targeting cognitive and neuropsychiatric symptoms will enable more successful recovery of bTBI veterans with persistent cognitive and neuropsychiatric symptoms. We base our hypothesis on the premise that neuromodulation (LED) treatment can improve compromised cellular activity of the brain tissue that has been damaged by blast exposure, and reduce neuroinflammation associated with TBI, which can induce long-lasting changes in the brain function and produce therapeutic behavioral outcome. Aims: (1) To probe efficacy of the novel neuromodulation treatment in bTBI veterans with persistent cognitive symptoms; (2) identify neurobiological markers that might predict treatment outcome, using neuropsychological, biological and physiological measures; and (3) determine if the observed improvements translate into real-world functional improvement in returning veterans with bTBI post-treatment. Study design: Veterans with mild bTBI will be divided, using a blocked randomization procedure into 2 groups: (G1) active LED treatment group, (G2) sham LED treatment. All participants will receive real or sham LED treatments 2 x week for 6 weeks. All participants will undergo the assessments at baseline (T1), immediately post-treatment (T2), one month post- (T3) and three months post-treatment (T4) to determine durability of the intervention. Each assessment will consist of neuropsychological tests, sleep, mood and stress measures, physiological measures, and functional outcome questionnaires. Significance: The proposed study will investigate the effects of a novel neuromodulation treatment (LED) and its effects on cognitive functioning, sleep, emotional functioning and quality of life in veterans with bTBI. This project will address the current therapeutic gap in the field of neurorehabilitation. Th proposed multi-modal approach to identifying neurobiological markers will provide important diagnostic and prognostic predictors in veterans with bTBI and associated neuropsychiatric problems. Development and evaluation of treatment programs for TBI are particularly important for helping the returning veterans with TBI to improve their independence and self-sufficiency, and to facilitate their community reintegration.